Has anyone upgraded a Red Hat 9 machine to any CentOS release? Any ideas on how to do it...
At present Red Hat/CentOS does not support upgrading from one release to another.
Upgrading from a version dating before the first release of RHEL/CentOS to any recent and supported version will present a lot of challenges.
Your best option is to install a new system with a recent release of CentOS next to your existing system and migrate your data/applications one by one.
It all depends on what you are using the system for. e.g. apache, mysql, python, perl have all released major updates included in recent releases that are often not backwards compatible.
The closest would be CentOS 3. You can try replacing